West Beleriand, showing the Falas, between Ered Wethrin and the River Nenning.

[They left Vinyamar, travelling] westward of the steep slopes of Taras, and across the great cape. There once the road from Nevrast to Brithombar had passed.... So they came into Beleriand, and the north region of the Falas; and turning eastward they sought the dark eaves of Ered Wethrin....

Unfinished Tales, Part 1, Ch 1, Of Tuor and His Coming to Gondolin

[The] realm of Nargothrond extended also west of Narog to the River Nenning, that reached the Sea at Eglarest; and Finrod became the overlord of all the Elves of Beleriand between Sirion and the sea, save only in the Falas. There dwelt those of the Sindar who still loved ships, and Círdan the shipbuilder was their lord; but between Círdan and Finrod there was friendship and alliance, and with the aid of the Noldor the havens of Brithombar and Eglarest were built anew. Behind their great walls they became fair towns and harbours with quays and piers of stone. Upon the cape west of Eglarest Finrod raised the tower of Barad Nimras to watch the western sea.... With the aid of the Elves of the Havens some of the folk of Nargothrond built new ships, and they went forth and explored the great Isle of Balar....

The Silmarillion, Quenta Silmarillion, Ch 14, Of Beleriand and its Realms

[The] Falathrim, the Elves of the Falas, who in after days had dwellings at the havens of Brithombar and Eglarest, [were] the first mariners in Middle-earth and the first makers of ships. Círdan the Shipwright was their lord.

The Silmarillion, Quenta Silmarillion, Ch 5, Of Eldamar and the Princes of the Eldalië

Now in [Thingol's] wide realm many Elves wandered free in the wild, or dwelt at peace in small kindreds far sundered; and only about Menegroth in the midst of the land, and along the Falas in the country of the mariners, were there numerous peoples.

The Silmarillion, Quenta Silmarillion, Ch 10, Of the Sindar

[The] Naugrim... went seldom to the Falas, for they hated the sound of the sea and feared to look upon it.

The Silmarillion, Quenta Silmarillion, Ch 10, Of the Sindar

[Morgoth's forces]... came down the rivers Brithon and Nenning and ravaged all the Falas, and besieged the walls of Brithombar and Eglarest. Smiths and miners and makers of fire they brought with them, and they set up great engines; and valiantly though they were resisted they broke the walls at last. Then the Havens were laid in ruin, and the tower of Barad Nimras cast down; and the most part of Círdan's people were slain or enslaved. But some went aboard ship and escaped by sea.... This remnant sailed with Círdan south to the Isle of Balar, and they made a refuge for all that could come thither....

[Though] the ancient dwellings of the Falathrim, Brithombar and Eglarest, were still far distant, Orcs now dwelt there and all the land was infested by the spies of Morgoth: he feared the ships of Círdan that would come at times raiding to the shores, and join with the forays sent forth from Nargothrond.

falas 'shore, line of surf' (Quenyafalassë) in Falas, Belfalas; also Anfalas in Gondor. Cf. Falathar, Falathrim. Another derivative from the root was Quenya falma '(crested) wave', Falmari, Mar-nu-Falmar.

In the map of Beleriand published in The Silmarillion, the Falas extend southwards almost to Arvernien. While the word falas can apply to any coastline (cf. Anfalas or Belfalas), the Falas — the realm of Círdan in West Beleriand — only extends to the border of Nargothrond at the Nenning. The map linked above has been adjusted to show the more limited extent of Círdan's realm.